The guy on the science TV shows would always use the dry-ice, dirt and water stirred up to create the steaming model of a comet.
We have proof now that they are correct.
When I first saw those closeup images of comet Hartley 2 from the spacecraft, I was actually wondering about all those spots on the image. Grainy image? A lot of hot pixels on the CCD? Or possibly stuff spewing off the comet?
Seems that it was spewing stuff! The comet is spitting out snowballs which are possibly between the size of a golf ball to a basketball in size. They are very light and fluffy, but at 27,000 mph, they could have still caused a big problem if the spacecraft was hit.